Whenever a particle or molecule is expanded into vacuum, the expansion imparts translational kinetic energy into the particle that monotonically increases with mass. For some analytical instruments that operate under vacuum, such translational kinetic energy may pose limitations on the capability of the analytical instrument. This is particularly true of mass spectrometers, in which the initial translational kinetic energy competes with the electric and magnetic fields of the mass spectrometer such that the instrumental resolution is adversely affected by the translational kinetic energy that the particle acquires in the process of expansion into vacuum.
The greater the mass of the particle, the greater the expansion induced kinetic energy. But the energy imparted to the particle through the electromagnetic field is proportional only to the charge of the particle and the magnitude of the electrical field, and is independent of the mass of the particle. As the mass of the particle increases, the effect of the expansion induced kinetic energy competes with, and eventually overwhelms, the effect of the electrical potential in the mass spectrometer that is applied to define the trajectory of charged particles. For this reason, it is very difficult to measure the mass of the large molecules or particles, e.g., molecules or particles having a molecular weight of 10 kDa, by mass spectrometry.
A prior art solution to this problem, as disclosed by U.S. Pat. No. 6,972,408 to Reilly, provides mass-dependent slowing of particles, i.e., the particles are slowed for a limited range of particle mass. The size or mass of the particles effectively slowed depends on the pressure of the reverse jet expansion.
In view of the above, there exists a need for a particle inlet system into the vacuum environment that provides a reduction of expansion-induced kinetic energy with a reduced mass dependence, and methods of operating the same.
Further, there exists a need for a particle inlet system into vacuum environment that provides a large range of particles masses to be slowed for subsequently introduction into the vacuum environment such as a mass spectrometer, and methods of operating the same.